Art of purifying rubber.



clear, and exact description of-t ing rubber and consists citizen HARRY O. CHUTE, OF CLEVELANROHIO.

ART OF -IURIIEYIN G RUBBER.

Specification of Letters Patent.

1 atented June 9, 1908.

Application filed October 21, 1907. Serial No. 398,384.

To all whom it may concern."

Be it known that I, HARRY OL'CHUTE, a of the United States, residing at Cleveland, Cuyahoga county,'State of Ohio,

. haveinventedcertainnewandusefullmprovements in the Art of Purifying Rubber and I do hereby declare the followin to be a full, e same, such art to which pertains to practice and use the same.

his invention relates to the art of purifyin a method of purifying crude rubber, said method comprising the treatment of .crude rubber by a compound solventconsisting of an acetic ester as will enable others skilled in the 1t a protected from. hydrolysis by an admixture of its dissociation products, or one of them;-

. all as more fully hereinafter set forth and as claimed. Y

Crude'rubbers,;and particularly those of the poorer grades,contain relatively large amounts of i urities, this being particularly true of t e rubbers from the' newer sources, such as pontianak, or dead borneo, guayule, Africans and a number of the .extracted rubbers. Better, grade rubbershowever also containmore orless'impurity which may beremoved. The impurities ordinarily found comprise in addition'to moisture, which frequently exists in rather,

large quantity and is diflicult and expensive 1 to remove by dryin'gimethods, considerable quantities of resins/some fat and extractive from vegetable Inaterials by the use of hydrocarbon solvent, there .is also usually some residual hydrocarbon. The amount of water is occasionally quite large, as for. instance in crude pontlanak, some samples of which contain as high as. 60. per cent. of water to only.

about 10 per cent. of real rubber, the residue being malnly resin. Guayules often contain a third of their wei ht as resin, water and other impurities. n thepurification of these wet, resinous rubbers byextraction with solvents it is of course necessary in practice tochoose a solvent in which rubber itself is substantially insoluble while Water, resin, fat andhydrocarbon oils will dissolve. This combination of-properties it is difficult to find in any single solvent. The acetic esters, orthe compounds of acetic acid with the lower alcohols, come nearest the ideal, ethyl acetate, for instance, being at once a solvent for resins, hydrocarbons, and, to some extent, for water, while rubber is very to produce the desired result. I .can therefore be protected against hydrolysis glacial acetic acid has forded by' the alcohol and an acid with elimination of water are prone to undergo the reverse transforma tion and take up water to re-fornl acid and alcohol, this being particularly the case when such esters are heated in a moist'coildition, as in distilling after use in treating moist rubbers. This liability to decom osition makes the acetic esters per se rather ss advantageous for use in treating wetlubbers. In recovering the esters after use they are apt to hydrolyze more or less in the still, causing a loss of solvent'and rendering it necessary to use stills of acid-resisting-niaterial.

It is the object of the present invention to use theseesters in aprotected form that is, in admixture with another solvent which will exercise a protective actionagainst hydrolysis of such esters, simultaneously converting them into compound solvent-s" better adapted in point of solvent power for the present purposes. It has been found that these esters do not hydrolyze with Water to an unlimited extent but that the decomposition goes for- 7 Ward to a certain limiting amount; to a point where a certain balance. exists between the amounts of undecomposed esters, acid, alcohol and water; and'that upon reaching this point the hydrolysis ceases. Ethyl acetate can therefore be protected against such decom osition by the addition of acetic acid and'et yl'alcohol, itshydrolytic products, in

sufficient amount to obtain this balance.

But as a matter of practice,'it is found that it is not necessary to .add both hydrolytic products; that the presence of either one of them in the theoretical amount is sufiicient Ethyl acetate bv the-presence of either acetic acid or ethyl alcohol; A mixture of ethyl acetate and many advantages for the resent purposes, but in the embodiment of this inventionat present preferred, the protective substance is ethyl alcohol.

- Methylacetate may be protected by either acetic acid or methyl alco ol, methyl alcohol being at present preferred.

Asid'e from the protection to the ester afresence of the alcohol, the mixture of alcoii vantagesintreating rubber, The resence of the alcohol gives the ester betterso vent prop erties for water while not materially dlmin- 1 and ester has certain ad- 2 its solvent properties forresi'ni At the same time, in the resence of the alcohol, the solvent powerso, the ester for rubber itself are diminished to a negligible amount. The p 5 compound solvent iswell adapted to remove the residual hydrocarbonsin 1f extracted rubber. The compound solvent us'ed in the present invention may be. either'ethyl acetate protected by ethyl alcoholor methyl '10 acetate protected by .r'nethyl alcohol. iAllz four bodies may be used together if desired. Ethyl alcohol and ethylacetate having nearly the same'boiling point, amixture may be fractionated and otherwise treated in 001- umn stills as if it were a single body, while the p'rotective action of thealcohol allows the-mixture to be fractionatedlout of water without hydrol sis of the ester, and Withas much ease an This is of course a vital ationthe first portions of solvent usedon a sample of rubber always become charged with water.

The amount of ethylfalcoholrequired to I protect ethyl acetate from hydrolysis, or of methyl alcohol required to protect methyl acetate, is not great, though of course this amount depends somewhat on the .PI'OPOIF tion of-w'ater with which the compound'solent may be mixed. The more of-either alcohol is mixed with eitheracet'ate, the greater the miscibility of the compound sol vent with water and consequently the greateris the amount of water whichwill be taken -'up by a given' amount of such compound solvent; e. g., the more alcohol isrequired for protection. Ordinarily however'lQ per cent ...of"alcohol will serve as a sufficient pro- 40 tecti'on' and give a compeund'solventof the desirab'lequalities stated. In use, the resin extracted from the rubber appears to reinforce the protective action ofthe alcohol to some extent; Greater quantities of alcohol,

up to per cent. or more, may however be used in making the .-comp0un' d solvent for.

some pur ses. Ethyl acetate and ethyl acetate mixed with but a small proportionof ethyl alcohol are not as good for operating 50 upon very moist rubbers as ethyl acetate mixed with greater proportions of ethyl alcohol. The ethyl acetate ishowever desirable in greater proportion when the deresini-' fying action is primarily desired sinceethyl acetate is one of the best solvents for rubber.

resin and while its admixtures with ethyl alcohol have a greater solvent power apparently than the average solvent power of the two bodies, yet the solvent power of the ester is so much greater that for deresinifying it is desirable usually to have not much more alcohol than is necessary for protection of the acetate. against hydrolysis. Boiling ethyl acetate will dissolve upwards of 50 per cent. of some rubber resins while ethyl alcohol will -moved bythe solvent directly ifso desired, the alcohol acting' to protect the'estenl 1n;-

certainty as alcohol alone. oint in the treat ment of crude, undried ru her in whichoper- 'drolysis of the particular; ester used, or it tillation orby fractional distillation asthel :seo,217

dissolve but about 8'per cent. of. thesame resins. Methyl-acetate has but about half drying the rubber'by the ordinary-methods,-

such as sheetingand drying in mower by i 'longcontinued exposure to dry air, more or less moist-ure will usually remain unless ex' 35 traordinary precautions be taken,particles-of moisture, belng inclosed the rubber substance.

In either compound solvent the alcohol employed may be that arising from thefhymay be reinforced by another alcohol. 7

' In the presentfpreferredembodiment of Y my process, I, add alcohol to an acetic ester. .toproduce 'thecompou'nd solvent and then wash the'rubber, dried or undried, with such r compound solvent, finally removing the solu- 1 tion of resin and other impurities to regain the solvent. The regainedsolvent may be againemployed in lieu of afresh mixturelofr its components. The-rubber-may be torn'or r disintegratedby any suitable'r'nech'anism-in., the(presence of the compound solvent. The use solventqnay be regained by'simple dis 1 characterof the liquid extract of the. rubber impurities'may indicate. If this extract cons tains much water, it is best fractionated. After treatment of the rubber, the adhering solvent may; be removed by'w'ashin'g with a. ittle water forming an aqueous so ution' ofuthe compound solvent from which such com ound solvent m'aybereadilyregained. .by istillation. In this'distillation' the :alcohol protects the ester. 7 On further wash-v ing the rubber'with morewater, using any of the ordinary mills or rolls for thispurpose,

removal of sticks, leaves, sand and other mechanical impurities can be'accomplished with extraordinary ease, the removal of the sticky resins leaving the riibbe-rfproper with but. little tendency to cling to foreign bodies.

; The completeness with which this subsequent mechanical purification canbe accomplished, is one of the great advantages in the use of my process. Apparently th e employment of my compound solvent leaves-the rubber.-; in better shape than doesthe use of the ester alone.

- I prefer the compound solvent arising 130 action. upon ethyl acetate.

from the admixture of ethyl alcohol with ethyl acetate, but for some rubbers the solvent formed by mixing methyl alcohol with methyl acetate is rather more advanta eous. The ethyl alcohol used may be or inary denatured spirit, the denaturing bodies ordinarily used, such as gasoline, benzine, wood spirit, acetone, etc., also havin a protective T e ethyl acetate may be made from such denatured spirit, the gasolene and other bodies mixing harmlessly and advantageously with the ester. The methyl alcohol used for making methyl acetate and for mixing with it may be the ordinary wood spirit, the presence of the methyl acetone, acetone, and other ketonoid bodies being advantageous rather than harmfulj Extraction of the rubber with the compound solvent is preferably facilitated by the action of heat, the hot compound solvent of course dissolving more resin than the cold.-

Cold extraction may however be performed, but it will involve the use of more solvent and more time. In the hot extraction of moist rubber, the presence of the protective alcohol prevents the liberation of acetic acid from the ester by hydrolysis and consequently corrosion ofv metallic containers.

What I claim is z:- 1. In the purification of rubber, the process which comprises producing a compound solvent containing an acetic ester and an alcohol and extracting rubber with the same.

2. In the purification of rubber, the process which comprises roducing a compound solvent containing et yl acetate and ethyl alcohol and extracting rubber with the same.

3. In the purification of rubber, the process which comprises mixing an alcohol with an acetic ester derived'frorn'such alcohol and 1 and an acetic ester.

6. In the purification of rubber, the process which com rises extracting rubber with a compound so vent containing ethyl alcohol and ethyl acetate.

7. In the purification of rubber, the process which comprises extracting rubber with an acetic ester protected against hydrolysis by anadmixture of one of its hydrolytic products.

8. In the purification of rubber, the process which comprises extracting rubber with a compound solvent comprising an acetic ester and a protecting substance.

In testimony whereof I aflix my signature, in the presence of two witnesses.

' HARRY O. CHUTE.

' Witnesses:

ALFRED M. HOUGHTON, RICHARD A. OURTIN. 

